Stability of co-continuous phase morphologies in emulsified polyethylene-polystyrene blends

The kinetics of coalescence (disruption of the PE network) at high temperature is expected to be very sensitive to slight differences in the interfacial activity of various emulsifiers and further, to even minute differences in their structure. This approach is illustrated here by investigating the morphology as a function of annealing time at 180°C, of low density PE / PS (20/80) blends added with 10% of a pure or a tapered hydrogenated polybutadiene-b-polystyrene ( HPB-b-PS ) block copolymer respectively. In order to characterize and quantify the morphological evolution of these blends, classical mathematical treatment of microscopic images as well as multiscaling analysis were used. These results clearly and quantitatively demonstrate that a tempered HPB-bPS block copolymer is definitely more efficient than the corresponding pure diblock for stabilizing the co-continuous structure of LDPE/PS blends rich in PS (80 %) at high temperature (180°C). Even after 90 min at that temperature, co-continuity of phases is not disturbed, whereas apparent phase size is only slightly increased. On the other hand, disruption of co-continuity and phase coalescence appear rapidly (after 5 min) in blends emulsified by the pure block copolymer.